In a semiconductor device manufacturing process, different kinds of processing such as film-forming and etching are repeatedly performed with respect to a substrate such as a semiconductor wafer or the like. In a semiconductor manufacturing apparatus for performing the processing, a substrate processing system provided with a plurality of processing chambers is used. The substrate processing system includes one or more transfer devices for transferring substrates between the processing chambers within the system and delivering substrates to another substrate processing system.
In the substrate transfer control technology used in the substrate processing system, it has been proposed to improve the transfer efficiency and throughput of a system as a whole by avoiding the likelihood of collision of the substrate loading/unloading timings between processing chambers each having an independent processing time. In this proposal, the cycle time is obtained by summing up the stay time during which one substrate stays within a module and the attendant busy time during which the function of each of the processing chambers is stopped due to the stay of the substrate before and after the stay. The cycle time is set in a substantially equal length with respect to the processing chambers. When gaining access to the respective processing chambers, the processed substrate is unloaded and a subsequent substrate is loaded to replace the processed substrate with the subsequent substrate. The simultaneous replacement of the substrates in the processing chambers is referred to as a pick-and-place transfer.
In the substrate processing system, a transfer control has also been proposed to perform in such a way that, even if a problem occurs in some of processing chambers, a substrate can be transferred to other normal processing chambers. In this proposal, if a problem in a destination processing chamber is detected while a substrate is transferred by a transfer device, the transferring substrate is moved to a standby port. That is, the transfer device is controlled so as to transfer a substrate to a processing chamber with no problem.
Moreover, the transfer control of a serial transfer has been proposed so that a single substrate is sequentially transferred to a plurality of processing chambers. In this proposal, if an unusable processing chamber is generated before a transfer means gains access to a processing chamber existing at the upstream end of a transfer cycle, the transfer cycle is allowed to proceed until the prior substrate can be unloaded from a changed destination processing chamber. If an unusable processing chamber is generated when the transfer means is positioned at the upstream side of the unusable processing chamber in the transfer cycle, the transfer means may stop a transfer operation until the prior substrate can be unloaded from a changed destination processing chamber.
In addition, a transfer route has been proposed to optimize in conjunction with the timing for terminating the prohibition of loading a substrate into a processing chamber. In this proposal, the destinations of substrates accommodated within substrate accommodation ports are decided so that the substrates can be sequentially transferred to the normally-operated processing chambers. In this case, the destination of at least one of the substrates having predetermined destinations may be changed to a loading-prohibition-terminated processing chamber in conjunction with the timing for terminating the prohibition of loading a substrate into the processing chamber which has been subjected to the substrate loading prohibition.
If one of the processing chambers of the substrate processing system kept in a loading prohibition state for whatever reason is terminated from the loading prohibition, a substrate may immediately be loaded into the loading-prohibition-terminated processing chamber. This is advantageous in improving the throughput of the substrate processing in the substrate processing system because the loading-prohibition-terminated processing chamber can be used in an expedited manner. However, even if the substrate processing is carried out under the aforementioned condition in the transfer cycle including the loading-prohibition-terminated processing chamber, the processing efficiency of the substrate processing system as a whole is not improved as one expects. For example, as compared with the processing efficiency of a substrate processing system in which all the processing chambers are normally usable from the beginning, the processing efficiency of a substrate processing system including a the loading-prohibition-terminated processing chamber is definitely reduced even when the number of usable processing chambers remains the same. Study was conducted to investigate the cause for such reduced efficiency. In the pick-and-place transfer, if a new substrate is immediately loaded into the loading-prohibition-terminated processing chamber, it is necessary perform operations to unload substrates from the remaining processing chambers. In this case, the loading of the subsequent substrates is delayed in the remaining processing chambers in which operations to unload substrates are performed. In proportion thereto, the substrate processing is not carried out in the processing chambers or the substrate processing is delayed in certain processing chambers. As a result, the substrate processing time fluctuates and the collision of the substrate loading/unloading timings occurs between the processing chambers. Consequently, during the time when the transfer cycle is repeated in succession, the processing chambers stay empty or the processed substrates are left alone within the processing chambers. This reduces the efficiency of the substrate processing system as a whole.